Chlorinated hydrocarbons such as 1,1,2,3-tetrachloropropene (HCO-1230xa) are useful feedstocks for manufacturing refrigerants, blowing agents, biocides, and polymers. For example, 1,1,2,3-tetrachloropropene is useful in the manufacture of herbicide trichloroalkyl diisopropyl thiocarbamate, commonly referred to as “triallate”.
More recently, as disclosed in U.S. Pat. No. 8,058,486, 1,1,2,3-tetrachloro-propene (HCO-1230xa) is useful as a starting raw material to produce 2,3,3,3-tetrafluoropropene (HFO-1234yf). HFO-1234yf is a low GWP molecule that can be used as an effective refrigerant, fire extinguishing agent, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric agent, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid, to name a few. This patent is hereby incorporated herein by reference.
Conventionally, 1,1,2,3-tetrachloropropene (HCO-1230xa) is produced by the dehydrochlorination of 1,1,1,2,3-pentachloropropane (HCC-240 db) either in the presence of a caustic solution or in the presence of Lewis acid catalysts such as FeCl3, and AlCl3.
As disclosed in U.S. Pat. No. 4,650,914, HCC-240 db can be converted, using a caustic solution, into an isomeric mixture of 2,3,3,3-tetrachloropropene and 1,1,2,3-tetrachloropropene. As a final step, the 2,3,3,3-tetrachlorpropene can be isomerized to 1,1,2,3-tetrachloropropene in the presence of a Lewis acid isomerization catalyst such as FeCl3 in a separate reactor. This patent is hereby incorporated herein by reference.
As also disclosed in U.S. Pat. No. 4,650,914, HCC-240 db can be directly converted into 1,1,2,3-tetrachloropropene via a catalytic dehydrochlorination reaction in the presence of a dehydrochlorination catalyst such as FeCl3. During this process, the compound 2,3,3,3-tetrachloropropene is either not formed or it is immediately converted to the 1,1,2,3-tetrachloropropene via an isomerization reaction, catalyzed by the same FeCl3 catalyst.
Applicants have recognized that while Lewis acid catalysts such as FeCl3, and AlCl3 provide advantages over caustic solutions in the conversion of HCC-240 db to HCO-1230xa, the carried over metal ions such as Fe3+ and Al3+ can cause the HCO-1230xa to decompose and to form HCl during the step of purification such as distillation. The HCl formed in this process can partially dissolve in the desired HCO-1230xa, and as a result, the final HCO-1230xa product will be somewhat acidic, which can complicate its storage and transportation. Thus, there is a need for means by which HCl formation can be mitigated during the HCO-1230xa purification step. This invention provides a solution to this problem.